1. Field of the Invention
The present invention relates to a vehicle operation assisting system that assists a collision avoidance operation which a driver performs to avoid collision with an obstacle during traveling of a vehicle.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 11-348799 discloses a device which can effectively perform, in combination, avoidance of collision by automatic braking and avoidance of collision by a steering operation. Specifically, a control is performed to increase turn round ability of a vehicle to avoid an obstacle if there is a space for avoidance ahead of an own vehicle, and another control is performed to increase stability of the vehicle by giving up avoiding the obstacle if there is no space for avoidance ahead of the own vehicle, in the case where a steering operation by a driver is performed during automatic braking of the vehicle and the obstacle can be avoided by a turn round ability increasing control by vehicle behavior control means.
When a vehicle is brought into an under-steer state, and the driver increases the turn of a steering wheel to further turn around the vehicle, the steering operation of the driver is assisted by a steering actuator. However, if the driver performs a large and abrupt steering operation to avoid collision with an obstacle when the vehicle is in the under-steer state, excessive assist is performed due to the under-steer state and the steering angle becomes too large, leading to a possibility that the return operation after avoiding an obstacle becomes difficult.
Japanese Patent Application Laid-open No. 2004-352031 discloses a device which informs a driver that a vehicle approaches the turning limit by inhibiting increase of assist torque or decreasing the assist torque in accordance with the degree of the under-steer and the vehicle speed, when the vehicle approaches the turning limit of the under-steer and there is a fear of disturbing the vehicle behavior if the turn of the steering wheel is increased; and which suppresses increase of turn of the steering wheel to prevent disturbance of vehicle behavior.
In the above-described conventional devices, correction of the assist torque is not made in the over-steer state, and therefore, there is a possibility of the driver feeling a sense of discomfort; and when the avoidance operation of an obstacle is performed, there is a possibility that steering reaction force becomes large to inhibit a quick avoidance operation.
Japanese Patent Application Laid-open No. 2000-72021 discloses a power steering control device which controls a assist force for steering a vehicle in accordance with the traveling state. In this device, the assist force applied to steering in the direction opposite from the target steering angle direction is set to be small as compared with the assist force applied to steering in the target steering angle, thereby suppressing steering in the direction opposite from the target steering angle direction to prevent the vehicle from deviating from the road.
In a vehicle operation assisting device which assists a steering operation of a driver by operating a steering actuator, when the driver abruptly operates a steering wheel to perform collision avoidance as the vehicle almost contacts an obstacle, if excessive assist is performed by the steering actuator, there is a possibility that the steering-wheel turning becomes excessively smooth to induce disturbance of vehicle behavior and gives a feeling of discomfort to the driver.